arXiv subjects

Somaditya Sen

Publications and source records attributed to Somaditya Sen.

40 records · Page 3Linked to original sources

arXiv2017

Structural and ferroelectric properties of perovskite Pb(1-x)(K0.5Sm0.5)xTiO3 ceramics

PbTiO3 has the highest tetragonal distortion (c/a=1.064) and highest spontaneous polarization among perovskite titanates. But, it is hazardous and hence one needs to reduce Pb content by substituting or reducing Pb content for use in applications. Pb(1-x)(K0.5Sm0.5)xTiO3 (0&x&0.5) perovskite powders were synthesized by sol-gel process, where Pb2+ was replaced by a combination of K+10.5Sm+30.5 (equivalent charge and comparable ionic radius) providing an excellent substitution model to study changes in structural and electrical properties. Vibrational properties and dielectric properties are modified with substitution. A polar tetragonal to a nearly nonpolar cubic phase transition decreases to lower temperatures with substitution due to reduces the lattice strain with substitution. Ferroelectricity is retained even for x=0.5, which has a nearly cubic phase and makes the material technologically important.

cond-mat.mtrl-sci↗

arXiv2017

Structural and dielectric properties of Pb(1-x)(Na0.5Sm0.5)xTiO3 ceramics

A correlation between structure and vibrational properties related to a ferroelectric to paraelectric phase transition in perovskite Pb(1-x)(Na0.5Sm0.5)xTiO3 (PNST - x) polycrystalline powders is discussed. Substitution leads to reduction of tetragonality which is associated with a shift of the phase transition to lower temperatures. The nature of the phase transition gets diffused with increasing substitution.

cond-mat.mtrl-sci↗

arXiv2016

Importance of strain reduction in improvement of optical transmission and conductance in Si4+ doped ZnO: a probable new moisture resistant Transparent Conductive Oxide

Si doped ZnO has been reported to be a better conductor than pure ZnO. It is reported that carrier density increases and hence conductivity increases. However, the effect on optical transmission is yet not clear until our recent report [1]. Zn1-xSixO for x= 0, 0.013, 0.020 and 0.027 have been synthesized using sol-gel method (a citric acid-glycerol route) followed by solid state sintering. We found that there is a decrease in defect states due to Si doping. The correlation of strain to the decrement in vacancy sites is discussed in this report. In modern electronics and solar cell fabrication, transparent conductive oxides (TCOs) are important components which conduct electrically without absorbing visible light. Known TCOs are extremely costly and are composed of non-abundant elements. Search for new ecofriendly, cheap and sustainable TCOs has been a recent research of attraction. Keeping in mind that most solar cells are exposed to natural conditions, the humidity tolerance becomes a determining factor. We report that sensitivity to moisture decreases drastically while the conductivity and optical transparency increases with doping. The reduction of strain and improvement of transport properties results in increased conductivity of Si doped ZnO pellets, tempting us to envisage this material as a probable alternate TCO.

cond-mat.mtrl-sci↗

arXiv2013

Sharp Raman Anomalies and Broken Adiabaticity at a Pressure Induced Transition from Band to Topological Insulator in Sb2Se3

The nontrivial electronic topology of a topological insulator is thus far known to display signatures in a robust metallic state at the surface. Here, we establish vibrational anomalies in Raman spectra of the bulk that signify changes in electronic topology: an E2 g phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb2Se3 crystal. Our first-principles calculations confirm the electronic transition from band to topological insulating state with reversal of parity of electronic bands passing through a metallic state at the ETT, but do not capture the phonon anomalies which involve breakdown of adiabatic approximation due to strongly coupled dynamics of phonons and electrons. Treating this within a four-band model of topological insulators, we elucidate how nonadiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator.

cond-mat.mtrl-sci↗